The aforementioned devices include a pulse generator that monitors the patient's cardiac activity and generates high energy stimulation pulses when the heart presents a ventricular arrhythmia that is deemed likely to be treated. When the high energy lies between approximately 0.1 and 10.0 J, the therapy is known as “cardioversion” and the electric stimulation shock delivered is called “a cardioversion shock.” When the energy level is greater than approximately 10.0 J, the therapy is called “defibrillation” and the electric shock delivered is called a “defibrillation shock.”
The high energy shock must be delivered when a ventricular tachycardia (VT) is detected, provided that the condition detected as a VT condition is indeed a true VT condition, and not a supraventricular tachycardia (SVT) condition (or some other condition). Indeed, in the case of an SVT condition, the tachycardia is of an atrial origin and the therapy shock that would be delivered would be without effect because the electrode that delivers the defibrillation therapy or, if necessary, the stimulation (ATP) therapy, is not located in the atrium. Actually, these situations cover various forms of a heartbeat rate disorder: When in the presence of an abnormally fast heartbeat rate (i.e., a tachyarrhythmia), this disorder can be caused by a ventricular fibrillation (VF), a ventricular tachycardia (VT), a sinusal tachycardia (ST) or a supraventricular tachycardia (SVT). A supraventricular tachycardia disorder condition covers atrial tachycardia, atrial flutter and atrial fibrillation (AF).
Heart beat rate disorders can exist simultaneously, and in such case one speaks about “bi-tachycardia,” in particular, for example, the presence of an atrial fibrillation combined with a ventricular tachycardia.
The diagnosis of a tachycardia condition or disorder can be performed, in a way in itself known, starting from criteria such as the ventricular frequency, the stability of the ventricular intervals (RR intervals), the analysis of atrio-ventricular association (revealed by the stability of the PR intervals), and the mode of starting of tachycardia (the presence of an abrupt acceleration in the rate and the cavity of origin, ventricular or atrial). One will be able in particular to refer to the EP-A-0 626 182 and its counterpart U.S. Pat. No. 5,462,060, both commonly assigned to the assignee hereof, Ela Médical, which describes a basic algorithm for the detection and classification of the tachyarhythmia, which U.S. patent is incorporated herein by reference. This algorithm has been implemented in the commercial products sold under the Defender™ and Alto™ brands and available from Ela Médical, Montrouge France.
The EP-A-0 838 235 and its counterpart U.S. Pat No. 5,868,793, and the EP-A-0 813 888 and its counterpart U.S. Pat No. 5,891,170 (both assigned to Ela Medical), describe various improvements of the basic algorithm, making it possible to improve further the discrimination between VT and SVT, in particular to avoid false positive diagnoses, i.e., an indication of a VT whereas it was actually a SVT, or false negative diagnoses, i.e., an indication of an SVT whereas it was actually a VT. The U.S. Pat. Nos. 5,868,793 and 5,891,170 are incorporated herein by reference in their entirety.